var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
    a256 = '',
    r64 = [256],
    r256 = [256],
    i = 0;

var UTF8 = {

    /**
     * Encode multi-byte Unicode string into utf-8 multiple single-byte characters
     * (BMP / basic multilingual plane only)
     *
     * Chars in range U+0080 - U+07FF are encoded in 2 chars, U+0800 - U+FFFF in 3 chars
     *
     * @param {String} strUni Unicode string to be encoded as UTF-8
     * @returns {String} encoded string
     */
    encode: function (strUni) {
        // use regular expressions & String.replace callback function for better efficiency
        // than procedural approaches
        var strUtf = strUni.replace(/[\u0080-\u07ff]/g, // U+0080 - U+07FF => 2 bytes 110yyyyy, 10zzzzzz
            function (c) {
                var cc = c.charCodeAt(0);
                return String.fromCharCode(0xc0 | cc >> 6, 0x80 | cc & 0x3f);
            })
            .replace(/[\u0800-\uffff]/g, // U+0800 - U+FFFF => 3 bytes 1110xxxx, 10yyyyyy, 10zzzzzz
                function (c) {
                    var cc = c.charCodeAt(0);
                    return String.fromCharCode(0xe0 | cc >> 12, 0x80 | cc >> 6 & 0x3F, 0x80 | cc & 0x3f);
                });
        return strUtf;
    },

    /**
     * Decode utf-8 encoded string back into multi-byte Unicode characters
     *
     * @param {String} strUtf UTF-8 string to be decoded back to Unicode
     * @returns {String} decoded string
     */
    decode: function (strUtf) {
        // note: decode 3-byte chars first as decoded 2-byte strings could appear to be 3-byte char!
        var strUni = strUtf.replace(/[\u00e0-\u00ef][\u0080-\u00bf][\u0080-\u00bf]/g, // 3-byte chars
            function (c) { // (note parentheses for precence)
                var cc = ((c.charCodeAt(0) & 0x0f) << 12) | ((c.charCodeAt(1) & 0x3f) << 6) | (c.charCodeAt(2) & 0x3f);
                return String.fromCharCode(cc);
            })
            .replace(/[\u00c0-\u00df][\u0080-\u00bf]/g, // 2-byte chars
                function (c) { // (note parentheses for precence)
                    var cc = (c.charCodeAt(0) & 0x1f) << 6 | c.charCodeAt(1) & 0x3f;
                    return String.fromCharCode(cc);
                });
        return strUni;
    }
};

while (i < 256) {
    var c = String.fromCharCode(i);
    a256 += c;
    r256[i] = i;
    r64[i] = b64.indexOf(c);
    ++i;
}

function code(s, discard, alpha, beta, w1, w2) {
    s = String(s);
    var buffer = 0,
        i = 0,
        length = s.length,
        result = '',
        bitsInBuffer = 0;

    while (i < length) {
        var c = s.charCodeAt(i);
        c = c < 256 ? alpha[c] : -1;

        buffer = (buffer << w1) + c;
        bitsInBuffer += w1;

        while (bitsInBuffer >= w2) {
            bitsInBuffer -= w2;
            var tmp = buffer >> bitsInBuffer;
            result += beta.charAt(tmp);
            buffer ^= tmp << bitsInBuffer;
        }
        ++i;
    }
    if (!discard && bitsInBuffer > 0) result += beta.charAt(buffer << (w2 - bitsInBuffer));
    return result;
}

var Plugin = function (dir, input, encode) {
    return input ? Plugin[dir](input, encode) : dir ? null : this;
};

Plugin.btoa = Plugin.encode = function (plain, utf8encode) {
    plain = Plugin.raw === false || Plugin.utf8encode || utf8encode ? UTF8.encode(plain) : plain;
    plain = code(plain, false, r256, b64, 8, 6);
    return plain + '===='.slice((plain.length % 4) || 4);
};

Plugin.atob = Plugin.decode = function (coded, utf8decode) {
    coded = coded.replace(/[^A-Za-z0-9\+\/\=]/g, "");
    coded = String(coded).split('=');
    var i = coded.length;
    do {
        --i;
        coded[i] = code(coded[i], true, r64, a256, 6, 8);
    } while (i > 0);
    coded = coded.join('');
    return Plugin.raw === false || Plugin.utf8decode || utf8decode ? UTF8.decode(coded) : coded;
};
module.exports = {
    btoa: Plugin.btoa,
    atob: Plugin.atob
}
